$$P V=k$$ for process $$B$$ and $$A$$.

$$\frac{P^{\gamma-1}}{T^\gamma}=k$$ for process $$B$$ and $$T=k$$ for process $$A$$.

$$\frac{T^\gamma}{P^{\gamma-1}}=k$$ for process $$A$$ and $$P V=k$$ for process $$B$$.

$$P V^{\prime}=k$$ for process $$B$$ and $$P V=k$$ for process $$A$$.

It is a restatement of the principle of conservation of energy

It is not applicable to any cyclic process

It introduces the concept of the entropy

It introduces the concept of the internal energy